Shulou(Shulou.com)11/24 Report--

CTOnews.com May 27, CTOnews.com learned from the University of Science and Technology of China that Pan Jianwei and Zhang Qiang of the University of Science and Technology of China, in cooperation with Wang Xiangbin of Tsinghua University, Liu Yang of Jinan Quantum Technology Research Institute, you Lixing and Zhang Weijun of Shanghai Institute of Microsystems of the Chinese Academy of Sciences, achieved 1002 km point-to-point long-distance quantum key distribution in optical fiber by developing low crosstalk phase reference signal control and extremely low noise single photon detectors. It not only sets a world record for the distance of optical fiber non-relay quantum key distribution, but also provides a scheme for high-speed backbone link of intercity quantum communication. The relevant research results were published in the international academic journal physical Review KuaiBao (Physical Review Letters) on May 25.

Based on the basic principles of quantum mechanics, quantum key distribution (QKD) can distribute keys securely among users. Combined with the encryption mode of "one secret at a time", quantum key distribution (QKD) can achieve secure communication with the highest security. However, the distance of quantum key distribution has been limited by the inherent loss of communication fiber and detector noise. Two-field quantum key distribution (TF-QKD) protocol makes use of the characteristic of single-photon interference to improve the relationship between bit rate and distance from the linear relationship of general quantum key distribution to the level of square root, so the coding distance can be much higher than that of general quantum key distribution schemes.

In this work, the research team adopted the "send-not send" two-field quantum key distribution protocol proposed by Wang Xiangbin et al., which can effectively improve the working distance of the quantum key distribution system under practical conditions. In order to carry out quantum key distribution over a very long distance, the research team cooperated with Changfei Optical Fiber and Cable Co., Ltd., using ultra-low loss fiber based on "pure silica core" technology to achieve a quantum channel fiber link of less than 0.16 dB / km. The Shanghai Institute of Microsystems, Chinese Academy of Sciences has developed a very low noise superconducting single photon detector. The noise of the single photon detector is reduced to 0.02 cps by multi-stage filtering in the temperature range of 40 K and 2.2 K. The research team also developed a dual-wavelength phase estimation scheme for time division multiplexing, which avoids noise effects such as secondary Rayleigh scattering of reference light at the same wavelength and spontaneous Raman scattering of reference light at different wavelengths, and reduces the link noise to less than 0.01 Hz.

Figure 1: long-distance quantum key distribution experimental system schematic diagram on the basis of the above technical development, this work has realized two-field quantum key distribution as far as 1002 km and achieved a bit rate of 0.0034 bps. After optimizing the system parameters, the bit rate of 47.06 kbps is obtained at 202 km fiber distance, and the bit rate obtained is 6 orders of magnitude higher than that of the original "measurement device independent" quantum key distribution at 300km and 400 km fiber distance. This work not only verifies the feasibility of the dual-field quantum key distribution scheme under extremely long distance, but also verifies that this protocol can achieve high bit rate quantum key distribution under the intercity optical fiber distance, which is suitable for the backbone link of intercity quantum communication. This work has been highly praised by reviewers as "an extremely important progress in this field and a new milestone in quantum key distribution technology (a significant advance for the field and a new landmark for QKD technology)".

Figure 2: code rate results of long-distance quantum key distribution experiment this research work has been supported by the Ministry of Science and Technology, the Natural Science Foundation, the Chinese Academy of Sciences, Shandong Province, Anhui Province and Shanghai.

CTOnews.com with paper link: https://link.aps.org/doi/10.1103/PhysRevLett.130.210801

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